Regenerative air conditioner

ABSTRACT

To avoid decline in the efficiency of a compressor at a low load, the thermal storage air conditioner has an operation controller which, if a rotational speed of the compressor is slowed down to a predetermined lower reference value in a simple cooling operation, switches operation of the thermal storage air conditioner from the simple cooling operation to a cooling and cold thermal energy storage operation to increase the rotational speed of the compressor. During the simple cooling operation refrigerant is condensed in the outdoor heat exchanger and evaporates in the indoor heat exchanger, and during a cooling and cold thermal energy storage operation the refrigerant is condensed in the outdoor heat exchanger, evaporates in the indoor heat exchanger, and the thermal storage medium in the thermal storage section is cooled by the refrigerant.

TECHNICAL FIELD

The present invention relates to a thermal storage air conditioner.

BACKGROUND ART

Air conditioners which cool and heat a room have been known. Patentdocument 1 discloses a thermal storage air conditioner using a thermalstorage medium. The thermal storage air conditioner has a refrigerantcircuit to which a compressor, an outdoor heat exchanger, and an indoorheat exchanger are connected, and a thermal storage section whichexchanges heat between a refrigerant in the refrigerant circuit and thethermal storage medium.

This air conditioner selectively performs: general cooling and heatingoperations in which a room is air conditioned without utilizing thermalstorage energy; a cold thermal energy storage operation in which thethermal storage medium is cooled to store cold thermal energy; acold-thermal-energy-utilization cooling operation in which the coldthermal energy stored in the thermal storage medium is utilized to coolthe room; and a thermal-energy-utilization heating operation in whichwarm thermal energy stored in the thermal storage medium is utilized toheat the room. During these operations, the compressor is actuated sothat the refrigerant circulates in the refrigerant circuit, therebyperforming a refrigeration cycle.

CITATION LIST Patent Document

Patent Document 1: Japanese Unexamined Patent Publication No. 2007-17089

SUMMARY OF THE INVENTION Technical Problem

In general, the air-conditioning capacity of an air conditioner iscontrolled by adjusting the rotational speed of a compressor. Thus, ifthe air-conditioning load (a cooling load or a heating load) in a roombecomes smaller during operation of the air conditioner, the rotationalspeed of the compressor is reduced to decrease the air-conditioningcapacity of the air conditioner according to the air-conditioning loadin the room. If the air conditioner has an excessive air-conditioningcapacity with respect to the air-conditioning load even after therotational speed of the compressor is set to a minimum value, an on/offoperation of the compressor, in which the halt and restart of thecompressor are repeated, is performed to prevent the room temperaturefrom becoming too low or too high.

In general, the efficiency of the compressor peaks at a certainrotational speed, and gradually decreases as the rotational speed isslowed down from the peak. Operation of the compressor at a relativelylow rotational speed may therefore decline the operational efficiency ofthe air conditioner. Moreover, the on/off operation of the compressor ata low air-conditioning load may increase a range of variations of theroom air temperature, and deteriorate the comfort of the room.

In view of the foregoing background, it is therefore an object of thepresent invention to reduce the decline of efficiency of an airconditioner and deterioration of the comfort of a room at a lowair-conditioning load.

Solution to the Problem

A first aspect of the present disclosure is directed to a thermalstorage air conditioner which includes: a refrigerant circuit (11) whichhas a compressor (22), an outdoor heat exchanger (23), and an indoorheat exchanger (72) and performs a refrigeration cycle; and a thermalstorage section (60) which has a thermal storage medium and exchangesheat between the thermal storage medium and a refrigerant of therefrigerant circuit (11). The thermal storage air conditioner is capableof performing a simple cooling operation in which in the refrigerantcircuit (11), the refrigerant is condensed in the outdoor heat exchanger(23) and evaporates in the indoor heat exchanger (72), and a cooling andcold thermal energy storage operation in which in the refrigerantcircuit (11), the refrigerant is condensed in the outdoor heat exchanger(23) and evaporates in the indoor heat exchanger (72), and in which thethermal storage medium in the thermal storage section (60) is cooled bythe refrigerant. The thermal storage air conditioner has an operationcontrol section (100) which, if a rotational speed of the compressor(22) is slowed down to a predetermined lower reference value in thesimple cooling operation, switches an operation of the thermal storageair conditioner from the simple cooling operation to the cooling andcold thermal energy storage operation to increase the rotational speedof the compressor (22).

In the first aspect, the operation is switched to the cooling and coldthermal energy storage operation if the rotational speed of thecompressor (22) is slowed down and the efficiency of the compressordeclines in the simple cooling operation, in order to increase therotational speed of the compressor (22) and improve the efficiency ofthe compressor. Further, in the simple cooling operation, even if theload is lowered to an extent that requires an on/off operation, part ofthe cold thermal energy obtained through the refrigeration cycle isstored in the thermal storage section (60). Thus, the temperature of thecold thermal energy utilized to cool the air in the indoor heatexchanger (72) may be dropped to a value corresponding to the coolingload in the room without performing the on/off operation.

A second aspect of the present disclosure is an embodiment of the firstaspect. In the second aspect, the operation control section (100)switches the operation of the thermal storage air conditioner from thecooling and cold thermal energy storage operation to the simple coolingoperation to reduce the rotational speed of the compressor (22) if therotational speed of the compressor (22) increases to a predeterminedupper reference value in the cooling and cold thermal energy storageoperation.

The efficiency of the compressor declines also in a case where therotational speed is too high. Therefore, in the second aspect, if therotational speed of the compressor (22) reaches a predetermined upperreference value in the cooling and cold thermal energy storageoperation, the operation is switched to the simple cooling operation toreduce the rotational speed of the compressor (22). As a result, thecompressor may be actuated at a highly efficient rotational speed,thereby making it possible to keep the efficiency of the air conditionerhigh.

A third aspect of the present disclosure is an embodiment of the firstor second aspect. In the third aspect, when the operation controlsection (100) switches the operation of the thermal storage airconditioner from the simple cooling operation to the cooling and coldthermal energy storage operation, the rotational speed of the compressor(22) is increased by a value equal to a lowest rotational speed of thecompressor (22).

In the third aspect, when the operation of the thermal storage airconditioner is switched from the simple cooling operation to the coolingand cold thermal energy storage operation, the rotational speed of thecompressor is increased by a value equal to a lowest rotational speed ofthe compressor.

A fourth aspect of the present disclosure is directed to a thermalstorage air conditioner which includes: a refrigerant circuit (11) whichhas a compressor (22), an outdoor heat exchanger (23), and an indoorheat exchanger (72) and performs a refrigeration cycle; and a thermalstorage section (60) which has a thermal storage medium and exchangesheat between the thermal storage medium and a refrigerant of therefrigerant circuit (11). The thermal storage air conditioner is capableof performing a simple heating operation in which in the refrigerantcircuit (11), the refrigerant is condensed in the indoor heat exchanger(72) and evaporates in the outdoor heat exchanger (23), and a heatingand warm thermal energy storage operation in which in the refrigerantcircuit (11), the refrigerant is condensed in the in the indoor heatexchanger (72) and evaporates in the outdoor heat exchanger (23), and inwhich the thermal storage medium in the thermal storage section (60) isheated by the refrigerant. The thermal storage air conditioner has anoperation control section (100) which, if a rotational speed of thecompressor (22) is slowed down to a predetermined lower reference valuein the simple heating operation, switches an operation of the thermalstorage air conditioner from the simple heating operation to the heatingand warm thermal energy storage operation to increase the rotationalspeed of the compressor (22).

In the fourth aspect, the operation is switched to the heating and warmthermal energy storage operation if the rotational speed of thecompressor (22) is slowed down and the efficiency of the compressordeclines in the simple heating operation, in order to increase therotational speed of the compressor (22) and improve the efficiency ofthe compressor. Further, in the simple heating operation, even if theload is lowered to an extent that requires an on/off operation, part ofthe warm thermal energy obtained through the refrigeration cycle isstored in the thermal storage section (60). Thus, the temperature of thewarm thermal energy utilized to heat the air in the indoor heatexchanger (72) may be dropped to a value corresponding to the heatingload in the room without performing the on/off operation of thecompressor.

A fifth aspect of the present disclosure is an embodiment of the fourthaspect. In the fifth aspect, the operation control section (100)switches the operation of the thermal storage air conditioner from theheating and warm thermal energy storage operation to the simple heatingoperation to reduce the rotational speed of the compressor (22) if therotational speed of the compressor (22) increases to a predeterminedupper reference value in the heating and warm thermal energy storageoperation.

The efficiency of the compressor declines also in a case where therotational speed is too high. Therefore, in the fifth aspect, if therotational speed of the compressor (22) reaches a predetermined upperreference value in the heating and warm thermal energy storageoperation, the operation is switched to the simple heating operation toreduce the rotational speed of the compressor (22). As a result, thecompressor may be actuated at a highly efficient rotational speed,thereby making it possible to keep the efficiency of the air conditionerhigh.

A sixth aspect of the present disclosure is an embodiment of the fourthor fifth aspect. In the sixth aspect, when the operation control section(100) switches the operation of the thermal storage air conditioner fromthe simple heating operation to the heating and warm thermal energystorage operation, the rotational speed of the compressor (22) isincreased by a value equal to a lowest rotational speed of thecompressor (22).

In the sixth aspect, when the operation of the thermal storage airconditioner is switched from the simple heating operation to the heatingand warm thermal energy storage operation, the rotational speed of thecompressor is increased by a value equal to a lowest rotational speed ofthe compressor.

Advantages of the Invention

According to the first aspect, if the rotational speed of the compressor(22) is slowed down, the operation is switched from the simple coolingoperation to the cooling and cold thermal energy storage operation toincrease the rotational speed of the compressor (22). As a result, it ispossible to reduce the decline in the efficiency of the compressor (22),and further improve the efficiency of the thermal storage airconditioner as a whole. Further, since the on/off operations of thecompressor (22) are not necessary, it is possible to reduce variationsin the temperature of the indoor air and keep the comfort of the room,and reduce the power required to start up the compressor (22), as wellas the power consumption.

According to the second aspect, if the rotational speed of thecompressor (22) increases, the operation is switched from the coolingand cold thermal energy storage operation to the simple coolingoperation to slow down the rotational speed of the compressor (22). As aresult, it is possible to reduce the decline in the efficiency of thecompressor (22).

According to the fourth aspect, if the rotational speed of thecompressor (22) is slowed down, the operation is switched from thesimple heating operation to the heating and warm thermal energy storageoperation to increase the rotational speed of the compressor (22). As aresult, it is possible to reduce the decline in the efficiency of thecompressor (22). Further, since the on/off operations of the compressor(22) are not necessary, it is possible to reduce variations in thetemperature of the indoor air and keep the comfort of the room, andreduce the power required to start up the compressor (22), as well asthe power consumption.

According to the fifth aspect, if the rotational speed of the compressor(22) increases, the operation is switched from the heating and warmthermal energy storage operation to the simple heating operation to slowdown the rotational speed of the compressor (22). As a result, it ispossible to reduce the decline in the efficiency of the compressor (22).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a piping diagram generally illustrating a configuration of athermal storage air conditioner according to an embodiment of thepresent disclosure.

FIG. 2 is a view corresponding to FIG. 1 illustrating the behavior of asimple cooling operation.

FIG. 3 is a view corresponding to FIG. 1 illustrating the behavior of acold thermal energy storage operation.

FIG. 4 is a view corresponding to FIG. 1 illustrating the behavior of autilization cooling operation.

FIG. 5 is a view corresponding to FIG. 1 illustrating the behavior of acooling and cold thermal energy storage operation.

FIG. 6 is a view corresponding to FIG. 1 illustrating the behavior of asimple heating operation.

FIG. 7 is a view corresponding to FIG. 1 illustrating the behavior of awarm thermal energy storage operation.

FIG. 8 is a view corresponding to FIG. 1 illustrating a heating and warmthermal energy storage operation (1).

FIG. 9 is a view corresponding to FIG. 1 illustrating a heating and warmthermal energy storage operation (2).

FIG. 10 is a view corresponding to FIG. 1 illustrating a utilizationheating operation (1).

FIG. 11 is a view corresponding to FIG. 1 illustrating a utilizationheating operation (2).

FIG. 12 illustrates an example relationship between the rotational speedof a compressor and the efficiency of the compressor.

FIG. 13 is a graph for explaining first and second variants of theembodiment, and shows the power consumption, and the efficiency andoperation time of the thermal storage air conditioner, with respect tothe transition of the load factor relative to a rated capacity.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail belowwith reference to the drawings. The following embodiments are merelyexemplary ones in nature, and are not intended to limit the scope,applications, or use of the invention.

A thermal storage air conditioner (10) according to an embodiment of thepresent invention selectively performs cooling and heating of a room.The thermal storage air conditioner (10) stores cold thermal energy of arefrigerant in a thermal storage medium, and utilizes this cold thermalenergy for cooling. The thermal storage air conditioner (10) stores warmthermal energy of the refrigerant in the thermal storage medium, andutilizes this warm thermal energy for heating.

<General Configuration>

As illustrated in FIG. 1, the thermal storage air conditioner (10) iscomprised of an outdoor unit (20), a thermal storage unit (40), and aplurality of indoor units (70). The outdoor unit (20) and the thermalstorage unit (40) are installed outside of a room. The plurality ofindoor units (70) are installed in the room. For the sake ofconvenience, only one indoor unit (70) is illustrated in FIG. 1.

The outdoor unit (20) includes an outdoor circuit (21). The thermalstorage unit (40) includes an intermediate circuit (41). The indoor unit(70) includes an indoor circuit (71). In the thermal storage airconditioner (10), the outdoor circuit (21) and the intermediate circuit(41) are connected to each other via three communication pipes (12, 13,14), and the intermediate circuit (41) and the plurality of indoorcircuits (71) are connected to each other via two communication pipes(15, 16). Thus, the thermal storage air conditioner (10) forms arefrigerant circuit (11) in which a refrigerant filling the thermalstorage air conditioner (10) circulates to perform a refrigerationcycle. The thermal storage air conditioner (10) has a controller (100)(an operation control section) which controls various devices which willbe described later.

<Outdoor Unit>

The outdoor unit (20) includes an outdoor circuit (21) which forms partof the refrigerant circuit (11). A compressor (22), an outdoor heatexchanger (23), an outdoor expansion valve (24), and a four-wayswitching valve (25) are connected to the outdoor circuit (21). A firstsubcooling circuit (30) and an intermediate suction pipe (35) areconnected to the outdoor circuit (21).

[Compressor]

The compressor (22) of the present embodiment is a single-stagecompressor, and forms a compression section which compresses therefrigerant and discharges the compressed refrigerant. The compressor(22) has a casing (22 a), in which a motor and a compression mechanism(not shown) are housed. The compression mechanism of the presentembodiment is configured as a scroll compression mechanism. However, thecompression mechanism may be any one of various types such asoscillating piston, rolling piston, screw, and turbo compressors. Thecompression mechanism includes a compression chamber between aspiral-shaped fixed scroll and a movable scroll. The refrigerant iscompressed as the capacity of the compression chamber graduallydecreases. The motor of the compressor (22) has a variable operatingfrequency which is varied by an inverter section. That is, thecompressor (22) is an inverter compressor, the rotational frequency(i.e., the capacity) of which is variable.

[Outdoor Heat Exchanger]

The outdoor heat exchanger (23) is configured as a cross-fin-and-tubeheat exchanger, for example. An outdoor fan (26) is provided adjacent tothe outdoor heat exchanger (23). The outdoor heat exchanger (23)exchanges heat between the air transferred by the outdoor fan (26) andthe refrigerant flowing through the outdoor heat exchanger (23). Anoutside-air temperature sensor (S1), which detects a temperature ofoutdoor air, is provided adjacent to the outdoor heat exchanger (23).For the sake of convenience, the outside-air temperature sensor (S1) isshown in only FIG. 1 and omitted in the other drawings.

[Outdoor Expansion Valve]

The outdoor expansion valve (24) is arranged between a liquid-side endof the outdoor heat exchanger (23) and a connection end of thecommunication pipe (12). The outdoor expansion valve (24) is configured,for example, as an electronic expansion valve, and adjusts the flow rateof the refrigerant by changing the degree of opening of the valve.

[Four-Way Switching Valve]

The four-way switching valve (25) has first to fourth ports. The firstport of the four-way switching valve (25) is connected to the dischargepipe (27) of the compressor (22). The second port of the four-wayswitching valve (25) is connected to a suction pipe (28) (a low-pressuresuction portion) of the compressor (22). The third port of the four-wayswitching valve (25) is connected to a gas-side end of the outdoor heatexchanger (22). The fourth port of the four-way switching valve (25) isconnected to a connection end of the communication pipe (14).

The four-way switching valve (25) is configured to switch between astate in which the first port and the third port communicate with eachother and the second port and the fourth port communicate with eachother (i.e., a first state indicated by solid lines in FIG. 1) and astate in which the first port and the fourth port communicate with eachother and the second port and the third port communicate with each other(i.e., a second state indicated by broken lines in FIG. 1).

[First Subcooling Circuit]

The first subcooling circuit (30) includes a first introduction pipe(31) and a first subcooling heat exchanger (32). One end of theintroduction pipe (31) is connected between the outdoor expansion valve(24) and the connection end of the communication pipe (12). The otherend of the first introduction pipe (31) is connected to the suction pipe(28) of the compressor (22). In other words, the first introduction pipe(31) forms a low-pressure introduction pipe connecting a liquid line(L1) and the suction pipe (28) on the low-pressure side of thecompressor (22). Here, the liquid line (L1) is a channel extendingbetween the liquid-side end of the outdoor heat exchanger (23) and aliquid-side end of the indoor heat exchanger (72). A first decompressionvalve (EV1) and a first heat transfer channel (33) are connected to thefirst introduction pipe (31) sequentially from one end to the other endof the first introduction pipe (31). The first decompression valve (EV1)is configured, for example, as an electronic expansion valve, andadjusts the degree of subcooling of the refrigerant at the exit of thesecond heat transfer channel (34) by changing the degree of opening ofthe valve. The first subcooling heat exchanger (32) forms a first heatexchanger which exchanges heat between the refrigerant flowing throughthe second heat transfer channel (34) and the refrigerant flowingthrough the first heat transfer channel (33). The second heat transferchannel (34) is provided between the outdoor expansion valve (24) andthe connection end of the communication pipe (12), of the liquid line(L1) of the refrigerant circuit (11).

[Intermediate Suction Pipe]

The intermediate suction pipe (35) forms an intermediate suction portionwhich introduces a refrigerant with an intermediate pressure to thecompression chamber of the compressor (22) in the middle of compression.The starting end of the intermediate suction pipe (35) is connected tothe connection end of the communication pipe (13), and the terminal endof the intermediate suction pipe (35) is connected to the compressionchamber of the compression mechanism of the compressor (22). Theintermediate suction pipe (35) includes an inner pipe portion (36)located inside the casing (22 a) of the compressor (22). The internalpressure of the intermediate suction pipe (35) basically corresponds toan intermediate pressure between the high and low pressures of therefrigerant circuit (11). A first solenoid valve (SV1) and a check valve(CV1) are connected to the intermediate suction pipe (35) sequentiallyfrom the upstream to downstream side. The first solenoid valve (SV1) isan open/close valve for opening and closing the channel. The check valve(CV1) allows the refrigerant to flow in a direction (the arrow directionin FIG. 1) from a primary thermal storage channel (44) (which will bedescribed in detail later) toward the compressor (22), and prohibits therefrigerant from flowing in a direction from the compressor (22) towardthe primary thermal storage channel (44).

<Thermal Storage Unit>

The thermal storage unit (40) forms a junction unit which intervenesbetween the outdoor unit (20) and the indoor unit (70). The thermalstorage unit (40) includes an intermediate circuit (41) which forms partof the refrigerant circuit (11). A primary liquid pipe (42), a primarygas pipe (43), and the primary thermal storage channel (44) areconnected to the intermediate circuit (41). A second subcooling circuit(50) is connected to the intermediate circuit (41). The thermal storageunit (40) includes a thermal storage device (60).

[Primary Liquid Pipe]

The primary liquid pipe (42) forms part of the liquid line (L1). Theprimary liquid pipe (42) connects a connection end of the communicationpipe (12) and a connection end of the communication pipe (15). A secondsolenoid valve (SV2) is connected to the primary liquid pipe (42). Thesecond solenoid valve (SV2) is an open/close valve for opening andclosing the channel.

[Primary Gas Pipe]

The primary gas pipe (43) forms part of a gas line (L2). Here, the gasline (L2) is a channel extending between the fourth port of the four-wayswitching valve (25) and a gas-side end of the indoor heat exchanger(72). The primary gas pipe (43) connects a connection end of thecommunication pipe (14) and a connection end of the communication pipe(16).

[Primary Thermal Storage Channel]

The primary thermal storage channel (44) is connected between theprimary liquid pipe (42) and the primary gas pipe (43). One end of theprimary thermal storage channel (44) is connected between the connectionend of the communication pipe (12) and the second solenoid valve (SV2).A third solenoid valve (SV3), a preheating refrigerant channel (64 b), athermal storage expansion valve (45), a thermal storage refrigerantchannel (63 b), and a fourth solenoid valve (SV4) are connected to theprimary thermal storage channel (44) sequentially in a direction fromthe primary liquid pipe (42) to the primary gas pipe (43). The thirdsolenoid valve (SV3) and the fourth solenoid valve (SV4) are open/closevalves for opening and closing the channels. The thermal storageexpansion valve (45) is configured, for example, as an electronicexpansion valve, and adjusts the pressure of the refrigerant by changingthe degree of opening of the valve.

A first bypass pipe (44 a) which bypasses the thermal storage expansionvalve (45) is connected to the primary thermal storage channel (44). Afifth solenoid valve (SV5) is connected to the first bypass pipe (44 a)in parallel with the thermal storage expansion valve (45). The fifthsolenoid valve (SV5) is an open/close valve for opening and closing thechannel. A pressure release valve (RV) is connected to the primarythermal storage channel (44) in parallel with the thermal storageexpansion valve (45).

[Second Subcooling Circuit]

The second subcooling circuit (50) includes a second introduction pipe(51) and a second subcooling heat exchanger (52). One end of the secondintroduction pipe (51) is connected between the second solenoid valve(SV2) and a connection end of the communication pipe (15). The other endof the second introduction pipe (51) is connected to the primary gaspipe (43). The second introduction pipe (51) is connected to the primarygas pipe (43) between the junction of the primary thermal storagechannel (44) with the primary gas pipe (43) and the connection end ofthe communication pipe (16). A second decompression valve (EV2) and athird heat transfer channel (53) are connected to the secondintroduction pipe (51) sequentially from one end to the other end of thesecond introduction pipe (51). The second decompression valve (EV2) isconfigured, for example, as an electronic expansion valve, and adjusts adegree of subcooling of the refrigerant at the exit of the fourth heattransfer channel (54) by changing the degree of opening of the valve.The second subcooling heat exchanger (52) exchanges heat between therefrigerant flowing through the fourth heat transfer channel (54) andthe refrigerant flowing through the third heat transfer channel (53).The fourth heat transfer channel (54) is provided at a portion betweenthe second solenoid valve (SV2) and the connection end of thecommunication pipe (15), of the primary liquid pipe (42). The secondsubcooling circuit (50) forms a subcooler which prevents the refrigerantflowing through the communication pipe (15) from vaporizing and beingflushed in a utilization and cooling operation and a utilization andcold thermal energy storage operation, which will be described in detaillater.

[Other Pipes]

An intermediate junction pipe (46), a first branch pipe (47), a secondbranch pipe (48), and a third branch pipe (49) are connected to theintermediate circuit (41). One end of the intermediate junction pipe(46) is connected at a portion of the primary thermal storage channel(44) between the third solenoid valve (SV3) and the preheatingrefrigerant channel (64 b). The other end of the intermediate junctionpipe (46) is connected to the intermediate suction pipe (35) via thecommunication pipe (13). One end of the first branch pipe (47) isconnected to a portion of the primary thermal storage channel (44)between the thermal storage refrigerant channel (63 b) and the fourthsolenoid valve (SV4).

The other end of the first branch pipe (47) is connected to the primarygas pipe (43) between the junction of the primary thermal storagechannel (44) with the primary gas pipe (43) and junction of the secondintroduction pipe (51) with the primary gas pipe (43). The thirddecompression valve (EV3) is connected to the first branch pipe (47).The third decompression valve (EV3) is configured, for example, as anelectronic expansion valve, and adjusts the pressure of the refrigerantby changing the degree of opening of the valve. The degree of opening ofthe third decompression valve (EV3) is adjusted to prevent the pressureof the thermal storage heat exchanger (63) from becoming excessively lowdue to a difference between an evaporating pressure in the indoor heatexchanger (72) and a pressure in the primary gas pipe (43) caused by apressure loss of the communication pipe (16) and/or a head differencedepending on installation conditions of the indoor unit (70) and theoutdoor unit (20), in an operation in which the indoor heat exchanger(72) serves as an evaporator.

The second branch pipe (48) and the third branch pipe (49) are connectedto the primary liquid pipe (42) and the primary thermal storage channel(44) in parallel with each other. One end of the second branch pipe (48)and one end of the third branch pipe (49) are connected to portions ofthe primary thermal storage channel (44) between the thermal storagerefrigerant channel (63 b) and the fourth solenoid valve (SV4). Theother end of the second branch pipe (48) and the other end of the thirdbranch pipe (49) are connected to portions of the primary liquid pipe(42) between the second solenoid valve (SV2) and the junction of thesecond introduction pipe (51) with the primary liquid pipe (42). Thefourth decompression valve (EV4) is connected to the second branch pipe(48). The fourth decompression valve (EV4) is configured, for example,as an electronic expansion valve, and adjusts the pressure of therefrigerant by changing the degree of opening of the valve. A sixthsolenoid valve (SV6) is connected to the third branch pipe (49). Thesixth solenoid valve (SV6) is an open/close valve for opening andclosing the channel.

[Thermal Storage Device]

The thermal storage device (60) forms a thermal storage section in whichheat is exchanged between the refrigerant of the refrigerant circuit(11) and the thermal storage medium. The thermal storage device (60) hasa thermal storage circuit (61) and a thermal storage tank (62) connectedto the thermal storage circuit (61). The thermal storage device (60) hasthe thermal storage heat exchanger (63) and the preheating heatexchanger (64).

The thermal storage circuit (61) is a closed circuit in which thethermal storage medium filling the thermal storage circuit (61)circulates. The thermal storage tank (62) is a hollow cylindricalvessel. The thermal storage tank (62) may be an open vessel. The thermalstorage medium is accumulated in the thermal storage tank (62). Anoutflow pipe (65) (an outflow portion) is connected to an upper portionof the thermal storage tank (62) to allow the thermal storage medium inthe thermal storage tank (62) to flow out of the tank. An inflow pipe(66) (an inflow portion) is connected to a lower portion of the thermalstorage tank (62) to allow the thermal storage medium present outsidethe thermal storage tank (62) to flow into the thermal storage tank(62). In other words, in the thermal storage tank (62), the junction ofthe outflow pipe (65) is located higher than the junction of the inflowpipe (66). A preheating-side thermal storage channel (64 a), a pump(67), and a thermal storage-side thermal storage channel (63 a) areconnected to the thermal storage circuit (61) sequentially from theoutflow pipe (65) toward the inflow pipe (66).

The preheating heat exchanger (64) is configured to exchange heatbetween the thermal storage medium flowing through the preheating-sidethermal storage channel (64 a) and the refrigerant flowing through thepreheating refrigerant channel (64 b). The thermal storage heatexchanger (63) is configured to exchange heat between the thermalstorage medium flowing through the thermal storage-side thermal storagechannel (63 a) and the refrigerant flowing through the thermal storagerefrigerant channel (63 b). The pump (67) is configured to circulate thethermal storage medium in the thermal storage circuit (61).

The thermal storage circuit (61) is provided with a thermal storagemedium temperature sensor (S2) (a thermal storage medium temperaturedetector) at a channel between the thermal storage heat exchanger (63)and the thermal storage tank (62). Specifically, the thermal storagemedium temperature sensor (S2) is located at a position where thetemperature of the thermal storage medium in the inflow pipe (66) isdetected. The thermal storage medium temperature sensor (S2) also servesas an accumulation detector which detects a start of accumulation ofcrystals of clathrate hydrates in the thermal storage circuit (61). Theposition of the thermal storage medium temperature sensor (S2) is anon-limiting example, and the sensor (S2) may also be located at adifferent position of the thermal storage circuit (61). For the sake ofconvenience, the thermal storage medium temperature sensor (S2) is shownin only FIG. 1 and omitted in the other drawings.

[Thermal Storage Medium]

Now, the thermal storage medium filling the thermal storage circuit (61)will be described in detail. A thermal storage material in whichclathrate hydrates are generated when cooled, that is, a thermal storagematerial having flowability, is adopted as the thermal storage medium.Examples of the thermal storage medium include a tetra-n-butyl ammoniumbromide (TBAB) aqueous solution containing tetra-n-butyl ammoniumbromide, a trimethylolethane (TME) aqueous solution, and paraffin-basedslurry. For example, the state as an aqueous solution of a tetra-n-butylammonium bromide aqueous solution is maintained even if it is cooled ina stable manner and turns into a subcooled state in which thetemperature of the aqueous solution is lower than a temperature at whichhydrates are generated. However, once some trigger is given in thissubcooled state, the subcooled solution transitions to a solutioncontaining clathrate hydrates (i.e., transitions to slurry). That is,the subcooled state of the tetra-n-butyl ammonium bromide aqueoussolution is changed to the state of slurry with relatively highviscosity due to the generation of clathrate hydrates (hydrate crystals)made of tetra-n-butyl ammonium bromide and water molecules. Thesubcooled state as used herein refers to a state in which clathratehydrates are not generated and the state of the solution is maintainedeven when the thermal storage medium reaches a temperature lower than orequal to the temperature at which hydrates are generated. On the otherhand, the tetra-n-butyl ammonium bromide aqueous solution in the stateof slurry is changed to the state of liquid (i.e., a solution) withrelatively high flowability due to melting of the clathrate hydrates, ifthe temperature of the aqueous solution becomes higher, by heating, thanthe temperature at which the hydrates are generated.

In the present embodiment, a tetra-n-butyl ammonium bromide aqueoussolution containing tetra-n-butyl ammonium bromide is adopted as thethermal storage medium. In particular, it is recommended that thethermal storage medium has a concentration close to a harmonicconcentration. In the present embodiment, the harmonic concentration isset to about 40%. In this case, the temperature at which hydrates aregenerated in the tetra-n-butyl ammonium bromide aqueous solution isabout 12° C.

<Indoor Unit>

Each of the plurality of indoor units (70) includes the indoor circuit(71) which forms part of the refrigerant circuit (11). The plurality ofindoor circuits (71) are connected in parallel with each other betweenthe communication pipe (15) (a liquid pipe) and the communication pipe(16) (a gas pipe). The plurality of indoor circuits (71) and theabove-described primary thermal storage channel (44) are connected inparallel with one another between the liquid line (L1) and the gas line(L2). The indoor heat exchanger (72) and the indoor expansion valve (73)are connected to each indoor circuit (71) sequentially from the gas-sideend toward the liquid-side end.

[Indoor Heat Exchanger]

The indoor heat exchanger (72) is configured, for example, as across-fin-and-tube heat exchanger. An indoor fan (74) is providedadjacent to the indoor heat exchanger (72). The indoor heat exchanger(72) exchanges heat between the air transferred by the indoor fan (74)and the refrigerant flowing through the outdoor heat exchanger (23).

The indoor circuit (71) is provided with a refrigerant temperaturesensor (S3) at the liquid-side end of the indoor heat exchanger (72).The refrigerant temperature sensor (S3) is used to determine whetherconditions indicating that the refrigerant that has been condensed bythe indoor heat exchanger (72) has a high temperature, or conditionsindicating that said refrigerant has a low temperature, are establishedor not, in a simple heating operation, which will be described in detaillater. As a sensor used for this determination, an air temperaturedetection sensor which detects a temperature of flowing-out air afterbeing heat-exchanged with the refrigerant in the indoor heat exchanger(72) may also be used. For the sake of convenience, the refrigeranttemperature sensor (S3) is shown in only FIG. 1 and omitted in the otherdrawings.

[Indoor Expansion Valve]

The indoor expansion valve (73) is arranged between a liquid-side end ofthe indoor heat exchanger (72) and the connection end of thecommunication pipe (15). The indoor expansion valve (73) is configured,for example, as an electronic expansion valve, and adjusts the flow rateof the refrigerant by changing the degree of opening of the valve.

<Controller>

The controller (100) serves as an operation control section whichcontrols various devices. Specifically, the controller (100) switchesbetween ON and OFF states of the compressor (22), switches between thestates of the four-way switching valve (25), switches between openingand closing of each of the solenoid valves (SV1-SV6), adjusts the degreeof opening of each of the expansion valves (24, 45, 73) and thedecompression valves (EV1-EV4), switches between ON and OFF states ofthe fans (26, 74), switches between ON and OFF states of the pump (67),etc. The thermal storage air conditioner (10) is further provided withvarious types of sensors not shown. The controller (100) controls thevarious devices, based on values detected by these sensors.

<Operation of Thermal Storage Air Conditioner>

Operations of the thermal storage air conditioner (10) according to thepresent embodiment will be described. The thermal storage airconditioner (10) selectively performs a simple cooling operation, a coldthermal energy storage operation, a utilization cooling operation, acooling and cold thermal energy storage operation, a simple heatingoperation, a warm thermal energy storage operation, a heating and warmthermal energy storage operation, and a utilization heating operation.The controller (100) controls various devices to switch between theseoperations.

[Simple Cooling Operation]

In the simple cooling operation, the thermal storage device (60) isstopped, and the indoor unit (70) cools a room. In the simple coolingoperation illustrated in FIG. 2, the four-way switching valve (25) is inthe first state, and the second solenoid valve (SV2), the fourthsolenoid valve (SV4), and the fifth solenoid valve (SV5) among the firstto sixth solenoid valves (SV1-SV6) are open. The rest of the solenoidvalves are closed. The second decompression valve (EV2) and the fourthdecompression valve (EV4) are fully closed. The outdoor expansion valve(24) is fully open. The degrees of opening of the first decompressionvalve (EV1) and the indoor expansion valve (73) are appropriatelyadjusted. The compressor (22), the outdoor fan (26), and the indoor fan(74) are actuated. The thermal storage device (60) is not actuated sincethe pump (67) is stopped. In the simple cooling operation, therefrigerant circuit (11) performs a refrigeration cycle in which theoutdoor heat exchanger (23) serves as a condenser, the first subcoolingheat exchanger (32) as a subcooler, and the indoor heat exchanger (72)as an evaporator. In the simple cooling operation, the low-pressure gasline (L2) and the primary thermal storage channel (44) communicate witheach other. Liquid accumulation in the primary thermal storage channel(44) may thus be prevented.

The refrigerant discharged from the compressor (22) is condensed by theoutdoor heat exchanger (23). A large part of the condensed refrigerantflows through the second heat transfer channel (34), and the rest of thecondensed refrigerant is decompressed by the first decompression valve(EV1) and then flows through the first heat transfer channel (33). Inthe first subcooling heat exchanger (32), the refrigerant in the secondheat transfer channel (34) is cooled by the refrigerant in the firstheat transfer channel (33). The refrigerant which has flowed into theliquid line (L1) is decompressed by the indoor expansion valve (73), andthen evaporates in the indoor heat exchanger (72). The refrigerantflowing through the gas line (L2) merges with the refrigerant which hasflowed into the first introduction pipe (31), and is taken into thecompressor (22).

[Cold Thermal Energy Storage Operation]

In the cold thermal energy storage operation, the thermal storage device(60) is actuated to store cold thermal energy in the thermal storagemedium in the thermal storage tank (62). In the cold thermal energystorage operation illustrated in FIG. 3, the four-way switching valve(25) is in the first state, and the second solenoid valve (SV2), thethird solenoid valve (SV3), and the fourth solenoid valve (SV4) amongthe first to sixth solenoid valves (SV1-SV6) are open. The rest of thesolenoid valves are closed. The first to fourth decompression valves(EV1-EV4) are fully closed. The outdoor expansion valve (24) is fullyopen. The degree of opening of the thermal storage expansion valve (45)is appropriately adjusted. The compressor (22) and the outdoor fan (26)are actuated, and the indoor fan (74) is stopped. The thermal storagedevice (60) is actuated since the pump (67) is in operation. In the coldthermal energy storage operation, the refrigerant circuit (11) performsa refrigeration cycle in which the outdoor heat exchanger (23) serves asa condenser, the preheating heat exchanger (64) as a radiator (arefrigerant cooler), and the thermal storage heat exchanger (63) as anevaporator. In the cold thermal energy storage operation, a surplusrefrigerant may be held in the channel extending from the high-pressureliquid line (L1) to the indoor unit (70).

The refrigerant discharged from the compressor (22) is condensed by theoutdoor heat exchanger (23). The condensed refrigerant flows through thepreheating refrigerant channel (64 b) of the primary thermal storagechannel (44). In the preheating heat exchanger (64), the thermal storagemedium is heated by the refrigerant. Cores (fine crystals) of theclathrate hydrates which have flowed out of the thermal storage tank(62) are thus melted. The refrigerant cooled in the preheatingrefrigerant channel (64 b) is decompressed by the preheating heatexchanger (64), and then flows through the thermal storage refrigerantchannel (63 b). In the thermal storage heat exchanger (63), the thermalstorage medium is cooled by the refrigerant and evaporates. Therefrigerant which has flowed into the gas line (L2) from the primarythermal storage channel (44) is taken into the compressor (22). Thethermal storage medium cooled by the thermal storage heat exchanger (63)is accumulated in the thermal storage tank (62).

[Utilization Cooling Operation]

In the utilization cooling operation, the thermal storage device (60) isactuated, and the cold thermal energy of the thermal storage mediumstored in the thermal storage tank (62) is utilized to cool the room. Inthe utilization cooling operation illustrated in FIG. 4, the four-wayswitching valve (25) is in the first state, and the third solenoid valve(SV3), the fifth solenoid valve (SV5), and the sixth solenoid valve(SV6) among the first to sixth solenoid valves (SV1-SV6) are open. Therest of the solenoid valves are closed. The first decompression valve(EV1) and the fourth decompression valve (EV4) are fully closed. Theoutdoor expansion valve (24) is fully open. The degrees of opening ofthe second decompression valve (EV2) and the indoor expansion valve (73)are appropriately adjusted. The compressor (22), the outdoor fan (26),and the indoor fan (74) are actuated. The thermal storage device (60) isactuated since the pump (67) is in operation. In the utilization coolingoperation, the refrigerant circuit (11) performs a refrigeration cyclein which the outdoor heat exchanger (23) serves as a condenser, thepreheating heat exchanger (64), the thermal storage heat exchanger (63),and the second subcooling heat exchanger (52) as radiators (refrigerantcoolers), and the indoor heat exchanger (72) as an evaporator.

The refrigerant discharged from the compressor (22) is condensed by theoutdoor heat exchanger (23). The condensed refrigerant is cooled by thepreheating heat exchanger (64) of the primary thermal storage channel(44), passes through the first bypass pipe (44 a), and further cooled bythe thermal storage heat exchanger (63). A large part of the refrigerantwhich has flowed through the primary thermal storage channel (44) andthe third branch pipe (49) into the liquid line (L1) flows through thefourth heat transfer channel (54). The rest of the refrigerant isdecompressed by the second decompression valve (EV2) and then flowsthrough the third heat transfer channel (53). In the second subcoolingheat exchanger (52), the refrigerant flowing through the fourth heattransfer channel (54) is cooled by the refrigerant in the third heattransfer channel (53). The refrigerant cooled by the second subcoolingheat exchanger (52) is decompressed by the indoor expansion valve (73),and then evaporates in the indoor heat exchanger (72). The refrigerantflowing through the gas line (L2) merges with the refrigerant which hasflowed out of the second introduction pipe (51), and is taken into thecompressor (22).

[Cooling and Cold Thermal Energy Storage Operation]

In the cooling and cold thermal energy storage operation, the thermalstorage device (60) is actuated to store cold thermal energy in thethermal storage medium, and the room is cooled by the indoor unit (70).In the cooling and cold thermal energy storage operation illustrated inFIG. 5, the four-way switching valve (25) is in the first state, and thesecond solenoid valve (SV2), the third solenoid valve (SV3), and thefourth solenoid valve (SV4) among the first to sixth solenoid valves(SV1-SV6) are open. The rest of the solenoid valves are closed. Thefirst decompression valve (EV1), the third decompression valve (EV3) andthe fourth decompression valve (EV4) are fully closed. The outdoorexpansion valve (24) is fully open. The degrees of opening of the seconddecompression valve (EV2), the thermal storage expansion valve (45), andthe indoor expansion valve (73) are appropriately adjusted. Thecompressor (22), the outdoor fan (26), and the indoor fan (74) areactuated. The thermal storage device (60) is actuated since the pump(67) is in operation. In the refrigerant circuit (11) in the cooling andcold thermal energy storage operation, the outdoor heat exchanger (23)serves as a condenser, the preheating heat exchanger (64) and the secondsubcooling heat exchanger (52) as radiators (refrigerant coolers), andthe thermal storage heat exchanger (63) and the indoor heat exchanger(72) as evaporators.

The refrigerant discharged from the compressor (22) is condensed by theoutdoor heat exchanger (23). The condensed refrigerant flows through thesecond heat transfer channel (34) and is diverged into the primarythermal storage channel (44) and the primary liquid pipe (42). Therefrigerant in the primary thermal storage channel (44) is cooled by thethermal storage medium in the preheating heat exchanger (64), and isdecompressed by the thermal storage expansion valve (45). A large partof the refrigerant in the primary liquid pipe (42) flows through thefourth heat transfer channel (54), and the rest of the refrigerant isdecompressed by the second decompression valve (EV2) and then flowsthrough the third heat transfer channel (53). In the second subcoolingheat exchanger (52), the refrigerant flowing through fourth heattransfer channel (54) is cooled by the refrigerant in the third heattransfer channel (53). The refrigerant cooled by the second subcoolingheat exchanger (52) is decompressed by the indoor expansion valve (73),and then evaporates in the indoor heat exchanger (72). The refrigerantflowing through the gas line (L2) merges with the refrigerant which hasflowed out of the second introduction pipe (51), and is taken into thecompressor (22).

[Simple Heating Operation]

In the simple heating operation, the thermal storage device (60) isstopped, and the indoor unit (70) heats a room. In the simple heatingoperation illustrated in FIG. 6, the four-way switching valve (25) is inthe second state, and the second solenoid valve (SV2) among the first tosixth solenoid valves (SV1-SV6) is open. The rest of the solenoid valvesare closed. The first to fourth decompression valves (EV1-EV4) and thethermal storage expansion valve (45) are fully closed. The degrees ofopening of the indoor expansion valve (73) and the outdoor expansionvalve (24) are appropriately adjusted. The compressor (22), the outdoorfan (26), and the indoor fan (74) are actuated. The thermal storagedevice (60) is not actuated since the pump (67) is stopped. In thesimple heating operation, the refrigerant circuit (11) performs arefrigeration cycle in which the indoor heat exchanger (72) serves as acondenser, and the outdoor heat exchanger (23) as an evaporator. Theindoor expansion valve (73) controls the degree of subcooling of therefrigerant at the exit of the indoor heat exchanger (72).

The refrigerant discharged from the compressor (22) flows through thegas line (L2) and is condensed by the indoor heat exchanger (72). Therefrigerant which has flowed into the liquid line (L1) is decompressedby the outdoor expansion valve (24), and then evaporates in the outdoorheat exchanger (23) and is taken into the compressor (22).

[Warm Thermal Energy Storage Operation]

In a warm thermal energy storage operation, the thermal storage mediumin which warm thermal energy is stored is accumulated in the thermalstorage tank (62). In the warm thermal energy storage operationillustrated in FIG. 7, the four-way switching valve (25) is in thesecond state, and the third solenoid valve (SV3), the fourth solenoidvalve (SV4), and the fifth solenoid valve (SV5) among the first to sixthsolenoid valves (SV1-SV6) are open. The rest of the solenoid valves areclosed. The first to fourth decompression valves (EV1-EV4) and theindoor expansion valve (73) are fully closed. The degree of opening ofthe outdoor expansion valve (24) is appropriately adjusted. Thecompressor (22) and the outdoor fan (26) are actuated, and the indoorfan (74) is stopped. The thermal storage device (60) is actuated sincethe pump (67) is in operation. In the warm thermal energy storageoperation, the refrigerant circuit (11) performs a refrigeration cyclein which the thermal storage heat exchanger (63) and the preheating heatexchanger (64) serve as condensers, and the outdoor heat exchanger (23)as an evaporator.

The refrigerant discharged from the compressor (22) passes through thegas line (L2), dissipates heat in the thermal storage heat exchanger(63), passes through the first bypass pipe (44 a), and then furtherdissipates heat in the preheating heat exchanger (64). The refrigerantwhich has flowed out of the primary thermal storage channel (44) isdecompressed by the outdoor expansion valve (24), and then evaporates inthe outdoor heat exchanger (23) and is taken into the compressor (22).The thermal storage medium heated by the thermal storage heat exchanger(63) and the preheating heat exchanger (64) is accumulated in thethermal storage tank (62).

[Heating and Warm Thermal Energy Storage Operation]

In the heating and warm thermal energy storage operation, the thermalstorage device (60) is actuated to store warm thermal energy in thethermal storage tank (62), and the room is heated by the indoor unit(70). The heating and warm thermal energy storage operation is roughlygrouped into a first heating and warm thermal energy storage operation(hereinafter referred to as a heating and warm thermal energy storageoperation (1)) and a second heating and warm thermal energy storageoperation (hereinafter referred to as a heating and warm thermal energystorage operation (2)).

[Heating and Warm Thermal Energy Storage Operation (1)]

In the heating and warm thermal energy storage operation (1) illustratedin FIG. 8, the four-way switching valve (25) is in the second state, andthird solenoid valve (SV3), the fifth solenoid valve (SV5), and thesixth solenoid valve (SV6) among the first to sixth solenoid valves(SV1-SV6) are open. The rest of the solenoid valves are closed. Thefirst to fourth decompression valves (EV1-EV4) and the thermal storageexpansion valve (45) are fully closed. The degrees of opening of theindoor expansion valve (73) and the outdoor expansion valve (24) areappropriately adjusted. The compressor (22), the outdoor fan (26), andthe indoor fan (74) are actuated. The thermal storage device (60) isactuated since the pump (67) is in operation. In the warm thermal energystorage operation, the refrigerant circuit (11) performs a refrigerationcycle in which the indoor heat exchanger (72) serves as a condenser, thethermal storage heat exchanger (63) and the preheating heat exchanger(64) as radiators, and the outdoor heat exchanger (23) as an evaporator.

The refrigerant discharged from the compressor (22) flows through thegas line (L2), and all of the refrigerant flows through the indoor heatexchanger (72). In the indoor heat exchanger (72), the refrigerantdissipates heat to the indoor air and is condensed. All of therefrigerant condensed in the indoor heat exchanger (72) flows throughthe third branch pipe (49) and the thermal storage heat exchanger (63).In the thermal storage heat exchanger (63), the refrigerant dissipatesheat to the thermal storage medium, so that the thermal storage mediumis heated. The refrigerant which has flowed through the thermal storageheat exchanger (63) further dissipates heat to the thermal storagemedium in the preheating heat exchanger (64), and flows through theliquid line (L1). This refrigerant evaporates in the outdoor heatexchanger (23) and is taken into the compressor (22).

In this manner, all of the refrigerant condensed in the indoor heatexchanger (72) flows through the thermal storage heat exchanger (63) inthe heating and warm thermal energy storage operation (1). Thus, heat ofthe surplus refrigerant which is not used for heating the room may beutilized for storing warm thermal energy in the thermal storage medium.

[Heating and Warm Thermal Energy Storage Operation (2)]

In the heating and warm thermal energy storage operation (2) illustratedin FIG. 9, the four-way switching valve (25) is in the second state, andthe second solenoid valve (SV1), the third solenoid valve (SV3), thefourth solenoid valve (SV4), and the fifth solenoid valve (SV5) amongthe first to sixth solenoid valves (SV1-SV6) are open. The rest of thesolenoid valves are closed. The first to fourth decompression valves(EV1-EV4) are fully closed. The degrees of opening of the indoorexpansion valve (73) and the outdoor expansion valve (24) areappropriately adjusted. The compressor (22), the outdoor fan (26), andthe indoor fan (74) are actuated. The thermal storage device (60) isactuated since the pump (67) is in operation. In the warm thermal energystorage operation, the refrigerant circuit (11) performs a refrigerationcycle in which the indoor heat exchanger (72) and the thermal storageheat exchanger (63) serve as condensers, and the outdoor heat exchanger(23) as an evaporator.

The refrigerant discharged from the compressor (22) flows through thegas line (L2), and part of the refrigerant flows through the indoor heatexchanger (72) and the rest of the refrigerant flows through the primarythermal storage channel (44). In the indoor heat exchanger (72), therefrigerant dissipates heat to the indoor air and is condensed. Therefrigerant condensed in the indoor heat exchanger (72) flows throughprimary liquid pipe (42).

The refrigerant in the primary thermal storage channel (44) dissipatesheat to the thermal storage medium in the thermal storage heat exchanger(63) and is condensed. This refrigerant is a high-temperature andhigh-pressure gas refrigerant, which increases a temperature differencebetween the refrigerant and the thermal storage medium. The thermalstorage medium may thus be given the warm thermal energy withreliability. The refrigerant condensed by the thermal storage heatexchanger (63) merges with the refrigerant flowing through the primaryliquid pipe (42), and is decompressed by the outdoor expansion valve(24). The decompressed refrigerant evaporates in the outdoor heatexchanger (23) and is taken into the compressor (22).

In this manner, in the heating and warm thermal energy storage operation(2), the high-temperature and high-pressure gas refrigerant dischargedfrom the compressor (22) flows into both of the indoor heat exchanger(72) and the thermal storage heat exchanger (63) in a parallel manner,and is condensed in the respective heat exchangers. Thus, the warmthermal energy is reliably given to the thermal storage medium, whilecontinuing heating of the room.

[Utilization Heating Operation]

In the utilization heating operation, the thermal storage device (60) isactuated, and the warm thermal energy of the thermal storage mediumstored in the thermal storage tank (62) is utilized as heat ofvaporization of the low-pressure refrigerant. Heating loads may thus bereduced. The utilization heating operation is roughly grouped into afirst utilization heating operation (hereinafter referred to as autilization heating operation (1)) and a second utilization heatingoperation (hereinafter referred to as a utilization heating operation(2)).

[Utilization Heating Operation (1)]

The utilization heating operation (1) is performed under a condition inwhich a difference (MP−LP) is relatively small between a pressure (MP)of the refrigerant which evaporates in the thermal storage heatexchanger (63) and a pressure (LP) of the refrigerant which evaporatesin the outdoor heat exchanger (23). For example, this condition is metin a situation in a winter season in which a temperature of outside airis relatively high, but a temperature of the thermal storage medium inthe thermal storage circuit (61) of the thermal storage device (60) isrelatively low.

In the utilization heating operation (1) illustrated in FIG. 10, thefour-way switching valve (25) is in the second state, and the thirdsolenoid valve (SV3) and the fifth solenoid valve (SV5) among the firstto sixth solenoid valves (SV1-SV6) are open. The rest of the solenoidvalves are closed. The first decompression valve (EV1) and the outdoorexpansion valve (24) are fully open. The second decompression valve(EV2) and the third decompression valve (EV3) are fully closed. Thedegree of opening of the fourth decompression valve (EV4) and the indoorexpansion valve (73) are appropriately adjusted. The compressor (22) andthe indoor fan (74) are actuated, and the outdoor fan (26) is stopped.The thermal storage device (60) is actuated since the pump (67) is inoperation. In the utilization heating operation (1), the refrigerantcircuit (11) performs a refrigeration cycle in which the indoor heatexchanger (72) serves as a condenser, and the thermal storage heatexchanger (63) as an evaporator.

The refrigerant discharged from the compressor (22) flows through thegas line (L2) and is condensed by the indoor heat exchanger (72). All ofthe refrigerant which has flowed into the liquid line (L1) flows in thesecond branch pipe (48). In the second branch pipe (48), the refrigerantis decompressed to a low pressure by the fourth decompression valve(EV4). The decompressed refrigerant flows through the thermal storagerefrigerant channel (63 b) of the thermal storage heat exchanger (63),and absorbs heat from the thermal storage medium and evaporates. Therefrigerant which has evaporated in the thermal storage heat exchanger(63) passes through the first bypass pipe (44 a), flows through thepreheating refrigerant channel (64 b) of the preheating heat exchanger(64), and absorbs heat from the thermal storage medium and furtherevaporates. This refrigerant flows through the primary thermal storagechannel (44) and is diverged into the first introduction pipe (31) andthe outdoor heat exchanger (23). These refrigerants merge with eachother in the suction pipe (28) and is taken into the compressor (22).Thus, the pressure loss of the refrigerant, and hence the power toactuate the compressor (22), may be reduced. The refrigerant flowingthrough the first introduction pipe (31) flows through the firstsubcooling heat exchanger (32), which is not an air heat exchanger.Thus, heat loss is also small. In addition, even when the refrigerantflows through the outdoor heat exchanger (23), the heat loss is smallsince the outdoor fan (26) stays at rest. In this manner, the pressureloss and/or heat loss of the low-pressure gas refrigerant may be reducedin the utilization heating operation (1). In addition, the firstintroduction pipe (31) also serves as a low-pressure injection pipe forsubcooling of the refrigerant. The number of pipes may thus be reduced.

Note that in the utilization heating operation (1), only the outdoorexpansion valve (24), of the first decompression valve (EV1) and theoutdoor expansion valve (24), may be fully closed to allow thelow-pressure gas refrigerant to flow only to the first introduction pipe(31). Further, only the first decompression valve (EV1), of the firstdecompression valve (EV1) and the outdoor expansion valve (24), may befully closed to allow the low-pressure gas refrigerant to flow only tothe outdoor heat exchanger (23).

[Utilization Heating Operation (2)]

The utilization heating operation (2) is performed under a condition inwhich a difference (MP−LP) is relatively large between a pressure (MP)of the refrigerant which evaporates in the thermal storage heatexchanger (63) and a pressure (LP) of the refrigerant which evaporatesin the outdoor heat exchanger (23). For example, this condition is metin a situation in a winter season in which a temperature of outside airis relatively low, but a temperature of the thermal storage medium inthe thermal storage circuit (61) of the thermal storage device (60) isrelatively high.

In the utilization heating operation (2) illustrated in FIG. 11, thefour-way switching valve (25) is in the second state, the first solenoidvalve (SV1), the second solenoid valve (SV3), and the fifth solenoidvalve (SV5) among the first to sixth solenoid valves (SV1-SV6) are open.The rest of the solenoid valves are closed. The first to thirddecompression valves (EV1-EV3) are fully closed. The degrees of openingof the fourth decompression valve (EV4), the indoor expansion valve (73)and the outdoor expansion valve (24) are appropriately adjusted. Thecompressor (22), the outdoor fan (26), and the indoor fan (74) areactuated. The thermal storage device (60) is actuated since the pump(67) is in operation. In the utilization heating operation, therefrigerant circuit (11) performs a refrigeration cycle in which theindoor heat exchanger (72) serves as a condenser, and the thermalstorage heat exchanger (63), the preheating heat exchanger (64), and theoutdoor heat exchanger (23) as evaporators.

The refrigerant discharged from the compressor (22) flows through thegas line (L2) and is condensed by the indoor heat exchanger (72). Therefrigerant which has flowed into the liquid line (L1) is diverged intothe second branch pipe (48) and the primary liquid pipe (42). Therefrigerant in the second branch pipe (48) is decompressed by the fourthdecompression valve (EV4) to an intermediate pressure (between a highpressure and a low pressure in the refrigerant circuit (11)) and flowsinto the primary thermal storage channel (44). The refrigerant in theprimary thermal storage channel (44) is heated in the thermal storageheat exchanger (63) and the preheating heat exchanger (64) andevaporates. The evaporated refrigerant sequentially passes through theintermediate junction pipe (46), the communication pipe (13), and theintermediate suction pipe (35), and is taken into the compressionchamber of the compressor (22) in the middle of compression.

The refrigerant in the primary liquid pipe (42) is decompressed by theoutdoor expansion valve (24), evaporates in the outdoor heat exchanger(23), and is taken into the suction pipe (28) of the compressor (22). Inthe compression chamber of the compressor (22), the low-pressurerefrigerant taken through the suction pipe (28) is compressed to theintermediate pressure, mixed with the intermediate-pressure refrigeranttaken through the intermediate suction pipe (35), and then compressed tohave a high pressure.

The utilization heating operation (2) is performed under a condition inwhich the temperature of the outside air is low and the temperature ofthe thermal storage medium of the thermal storage circuit (61) of thethermal storage device (60) is relatively high. Thus, in the utilizationheating operation (2), the difference (MP−LP) between the evaporatingpressure MP of the refrigerant in the thermal storage heat exchanger(63) and the evaporating pressure LP of the refrigerant in the outdoorheat exchanger (23) is relatively large. Thus, in the middle of thecompression process in the compression chamber of the compressor (22),the possibility that the internal pressure of the compression chamberbecomes higher than the pressure of the refrigerant introduced thereinthrough the intermediate suction pipe (35) may be reduced, which allowsthe refrigerant in the intermediate suction pipe (35) to be reliablyintroduced in the compression chamber.

Moreover, the intermediate suction pipe (35) is provided with the checkvalve (CV1) which prohibits the backflow of the refrigerant from thecompressor (22) toward the primary thermal storage channel (44). Thus,even if the pressure MP of the refrigerant flowing out of theintermediate suction pipe (35) is lower than the internal pressure ofthe compression chamber in the middle of the compression process, therefrigerant in the compression chamber does not flow back into theintermediate suction pipe (35). The check valve (CV1) may be provided atthe inner pipe portion (36) of the intermediate suction pipe (35)located inside the casing (22 a) of the compressor (22). Thisconfiguration may achieve a minimum channel length from the compressionchamber of the compression mechanism in the middle of the compressionprocess to the check valve (CV1), and therefore a minimum dead volumethat does not contribute to the compression of the refrigerant. As aresult, a decline in the compression efficiency of compressor (22) maybe prevented.

Further, if the refrigerant is compressed under the condition in whichthe difference MP−LP is relatively large, the overall workloads requiredfor the compressor (22) to compress the refrigerant to a high pressureare reduced. As a result, the utilization heating operation (2) mayachieve energy-efficient heating, while giving the warm thermal energyof the thermal storage medium to the refrigerant.

[First Mode of Utilization Heating Operation]

In the above-described utilization heating operation (1) and/or theutilization heating operation (2), the controller (100) compares anoutside-air temperature To detected by the outside-air temperaturesensor (S1) (see FIG. 1) with a predetermined temperature Ta. If thedetected outside-air temperature To is higher than or equal to thepredetermined temperature Ta, the controller (100) determines that afirst condition is satisfied, and performs a first mode.

The first mode is a type of operation performed in the utilizationheating operation (1) and/or the utilization heating operation (2) inwhich the thermal storage medium heats the refrigerant via the thermalstorage heat exchanger (63) only when the temperature of the thermalstorage medium is higher than a temperature at which hydrates aregenerated. It can thus be said that, of sensible heat and latent heatstored in the thermal storage medium, only the sensible heat is used forheating in the first mode.

In the first mode, the relatively high sensible heat of the thermalstorage medium is given to the refrigerant via the thermal storage heatexchanger (63) and/or the preheating heat exchanger heat exchanger (64).Thus, even if heat is exchanged between the thermal storage medium andthe refrigerant, the evaporating pressure can be maintained at arelatively high pressure, and the efficiency of heating can be improved.However, in the first mode, the outside-air temperature To is high andthe evaporating pressure of the low-pressure refrigerant in the outdoorheat exchanger (23) is also high. Thus, if the first mode is maintainedand the temperature of the thermal storage medium in the thermal storagecircuit (61) gradually decreases, the evaporating pressure in thethermal storage circuit (61) also decreases. In this state, maintainingthe first mode no longer improves the efficiency of heating. To avoidsuch a situation, the controller (100) terminates the first mode whenthe temperature of the thermal storage medium detected by the thermalstorage medium temperature sensor (S2) is lower than a referencetemperature Tb, and controls devices to perform a simple heatingoperation. The reference temperature Tb used herein is a predeterminedtemperature higher than or equal to a temperature at which hydrates aregenerated (e.g., 12° C.).

In the simple heating operation (FIG. 6) thus performed, the pump (67)is stopped, so that the refrigerant does not flow through the thermalstorage heat exchanger (63). This means that the thermal storage mediumis not cooled by the refrigerant any more, and thus the temperature ofthe thermal storage medium will not be lower than or equal to thetemperature at which hydrates are generated. As a result,crystallization and accumulation of clathrate hydrates in the pipes ofthe thermal storage circuit (61) may be prevented, which may reliablyprevent clogging of the thermal storage circuit (61). Moreover, heatingof the room is maintained by the shift to the simple heating operation,and comfort of the room is not deteriorated.

[Second Mode of Utilization Heating Operation]

In the above-described utilization heating operation (1) and/or theutilization heating operation (2), the controller (100) determines thatthe first condition is not satisfied and performs a second mode ofoperation when the detected outside-air temperature To is lower than thepredetermined temperature Ta.

The second mode is a type of operation in which the thermal storagemedium continues to heat the refrigerant via the thermal storage heatexchanger (63) even after the temperature of the thermal storage mediumfalls below the temperature at which hydrates are generated. It can thusbe said that both sensible heat and latent heat stored in the thermalstorage medium are utilized for heating in the second mode.

In the second mode, the relatively low latent heat of the thermalstorage medium is given to the refrigerant via the thermal storage heatexchanger (63) and the preheating heat exchanger heat exchanger (68). Inthe second mode, the outside-air temperature To is low, and theevaporating pressure of the low-pressure refrigerant in the outdoor heatexchanger (23) is also low. Thus, the evaporating pressure can bemaintained at a relatively high pressure, and the efficiency of heatingcan be improved, by exchanging heat between the thermal storage mediumand the refrigerant.

If the second mode is maintained, the temperature of the thermal storagemedium in the thermal storage circuit (61) gradually decreases and fallsbelow the temperature at which hydrates are generated. As a result,clathrate hydrates may be generated and crystals of the hydrates mayaccumulate in the pipes of the thermal storage circuit (61). To avoidthis phenomenon, the thermal storage device (60) is configured to usethe thermal storage medium temperature sensor (S2) to detect start ofaccumulation of the crystals of the clathrate hydrates.

Specifically, the thermal storage medium of the thermal storage circuit(61) falls in a subcooled state, and hence crystals of the hydrates arenot generated, even when the temperature thereof falls below thetemperature at which hydrates are generated. However, the subcooledstate ends and hydrate crystals are generated, if the thermal storagemedium in the subcooled state is given some trigger such as impact. Ifthe subcooled state ends, the temperature of the thermal storage mediumincreases to a temperature close to the temperature at which hydratesare generated. If the thermal storage medium temperature sensor (S2)detects that the temperature of the thermal storage medium hasincreased, the controller (100) determines that the crystals ofclathrate hydrates start to accumulate. For example, a flow-ratedetector for detecting a circulating volume of the thermal storagemedium in the thermal storage circuit (61) may be used as anaccumulation detector for detecting the start of accumulation of thecrystals of clathrate hydrates. That is, it may be detected that thecrystals of clathrate hydrates start to accumulate when the flow-ratedetector detects that the circulating volume of the thermal storagemedium in the thermal storage circuit (61) is lower than a predeterminedvalue.

If the start of accumulation of crystals of the clathrate hydrates isdetected, the controller (100) stops the second mode and performs theheating and warm thermal energy storage operation. Specifically, if thestart of accumulation of crystals of the clathrate hydrates is detected,the controller (100) determines whether a condition indicating therefrigerant that has been condensed in the indoor heat exchanger (72)has a high temperature is met or not.

Specifically, a determination section of the controller (100) comparesthe temperature Tb of the refrigerant that has been condensed in theindoor heat exchanger (72) with a predetermined reference refrigeranttemperature Ts, when shifting the operation from the second mode to theheating and warm thermal energy storage operation. The determinationsection determines that the above condition is met if the temperature Tbof the refrigerant is higher than the reference refrigerant temperatureTs. In this case, the controller (100) controls the devices to performthe first heating and warm thermal energy storage operation (i.e., theheating and warm thermal energy storage operation (1)), as illustratedin FIG. 8. As a result, the heating and warm thermal energy storageoperation (1) is performed in which the entire amount of the refrigerantcompressed in the compressor (22) sequentially flows through the indoorheat exchanger (72) and the thermal storage heat exchanger (63). In theheating and warm thermal energy storage operation (1) performed underthis condition, the refrigerant which has flowed through the indoor heatexchanger (72) has a sufficiently high temperature. Thus, the thermalstorage medium can be well heated by the refrigerant, which allows formaintaining heating of the room.

On the other hand, suppose that the temperature Tb of the refrigerantcondensed in the indoor heat exchanger (72) is lower than or equal tothe reference refrigerant temperature Ts, when the operation is shiftedfrom the second mode to the heating and warm thermal energy storageoperation. In such a case, the determination section of the controller(100) determines that a condition indicating the refrigerant condensedin the indoor heat exchanger (72) has a high temperature is not met.Then, the controller (100) controls the devices to perform the secondheating and warm thermal energy storage operation (i.e., the heating andwarm thermal energy storage operation (2)), as illustrated in FIG. 9. Asa result, the refrigerant compressed by the compressor (22) is divergedinto both of the indoor heat exchanger (72) and the thermal storage heatexchanger (63), and evaporates in the respective heat exchangers. Thus,the temperature of the thermal storage medium can be reliably increased,while continuing heating of the room.

<Efficiency of Compressor and Switching of Operation>

Described below are the rotational speed of the compressor (22) and theefficiency of the compressor, and switching of the operation of thethermal storage air conditioner (10) in relation to these aspects of thecompressor (22).

[Efficiency of Compressor]

As explained in the description of the compressor (22), the motor of thecompressor (22) has a variable operating frequency which is varied by aninverter section, and a variable rotational speed. The efficiency of thecompressor (22) relies on the rotational speed of the compressor (22).FIG. 12 shows an example relationship between the rotational speed (rps)and the efficiency (%) of the compressor.

In the example shown in FIG. 12, the efficiency of the compressor is atthe peak near the rotational speed R. The efficiency of the compressorgradually declines as the compressor has a lower rotational speed thanR, and the compressor has the lowest efficiency at a rotational speedRmin. The efficiency of the compressor also declines when the rotationalspeed of the compressor is too high, and is lower at a rotational speedRmax than it is at R.

Thus, desirably, the compressor (22) is driven at a rotational speedwhich contributes to high efficiency of the compressor. In particular,it is recommended to avoid an extremely slow rotational speed of thecompressor, since the efficiency of the compressor quickly declines whenthe rotational speed is slowed down.

The air-conditioning capacity of the thermal storage air conditioner(10) is controlled by adjusting the rotational speed of the compressor(22). Thus, if the air-conditioning load (a cooling load or a heatingload) in a room is lowered during the operation of the thermal storageair conditioner (10), the rotational speed of the compressor (22) isreduced to decrease the air-conditioning capacity of the thermal storageair conditioner (10) according to the air-conditioning load in the room.

Conventionally, If the air conditioner has an excessive air-conditioningcapacity with respect to the air-conditioning load even after therotational speed of the compressor (22) is set to a minimum value (alowest rotational speed), an on/off operation of the compressor (22), inwhich the halt and restart of the compressor (22) are repeated, is usedto be performed to prevent the room temperature from becoming too low ortoo high. However, it is recommended to avoid the on/off operation sincethe on/off operation may increase the power consumption and/ordeteriorate the comfort due to frequent on/off switching of the airconditioning.

Instead, in the present invention, switching between the simple coolingoperation and the cooling and cold thermal energy storage operation (andswitching between the simple heating operation and the heating and warmthermal energy storage operation) is performed as will be describedbelow.

[Switching Between Simple Cooling Operation and Cooling and Cold ThermalEnergy Storage Operation]

If a cooling load in a room is lowered in the simple cooling operation,and the rotational speed of the compressor (22) is slowed down to apredetermined lower reference value R1, the controller (100) switchesthe operation of the thermal storage air conditioner (10) from thesimple cooling operation to the cooling and cold thermal energy storageoperation.

The lower reference value R1 is set to be larger than Rmin and smallerthan R. It is recommended that the lower reference value R1 be set to beslightly larger than Rmin.

In the simple cooling operation, only the indoor air in the indoor heatexchanger (72) is cooled, whereas in the cooling and cold thermal energystorage operation, both the indoor air in the indoor heat exchanger (72)and the thermal storage medium in the thermal storage heat exchanger(63) are cooled. Thus, the low pressure in the refrigeration cycletemporarily increases when the simple cooling operation is switched tothe cooling and cold thermal energy storage operation.

On the other hand, in the simple cooling operation and the cooling andcold thermal energy storage operation, the controller (100) adjusts therotational speed of the compressor (22) so that the low pressure in therefrigeration cycle (i.e., a pressure of the refrigerant taken into thecompressor) will be a predetermined target value. Thus, when the simplecooling operation is switched to the cooling and cold thermal energystorage operation, the rotational speed of the compressor (22) needs tobe increased to lower the low pressure in the refrigeration cycle to thetarget value.

To do this, the controller (100) of the present embodiment switches theoperation of the thermal storage air conditioner (10) from the simplecooling operation to the cooling and cold thermal energy storageoperation to increase the rotational speed of the compressor (22), ifthe rotational speed of the compressor (22) is slowed down in the simplecooling operation to the lower reference value R1, at which thecompressor (22) operates inefficiently. As a result, the rotationalspeed of the compressor (22) exceeds the lower reference value R1, andthe efficiency of the compressor (22) is improved.

Conventionally, If the thermal storage air conditioner (10) has anexcessive cooling capacity with respect to the cooling load of the roomeven after the rotational speed of the compressor (22) is set to aminimum value Rmin, an on/off operation of the compressor (22), in whichthe halt and restart of the compressor (22) are repeated, is used to beperformed to prevent the room temperature from becoming too low.

On the other hand, If the rotational speed of the compressor (22) isslowed down to the lower reference value R1 in the simple coolingoperation, the controller (100) of the present embodiment switches theoperation of the thermal storage air conditioner (10) from the simplecooling operation to the cooling and cold thermal energy storageoperation. With this control, the room can be cooled by utilizing onlypart of the cold thermal energy obtained by the refrigeration cycle, andthe amount of the cold thermal energy used to cool the indoor air in theindoor heat exchanger (72) can be reduced to an appropriate amount forthe cooling load in the room, while allowing the actuation of thecompressor (22) to keep running. Thus, according to the presentembodiment, avoiding the on/off operation of the compressor (22) allowsfor maintaining the comfort of the room high even in a state in whichthe cooling load of the room is very low.

The lower reference value R1, based on which the operation is switchedfrom the simple cooling operation to the cooling and cold thermal energystorage operation, is determined from the relationship between therotational speed and the efficiency of the compressor as shown in FIG.12, a rotational speed of the compressor (22) for storing cold thermalenergy, and any other suitable parameters. The amount of cold thermalenergy stored in the thermal storage section (60) may also be used as aparameter based on which the lower reference value is determined.

Now, if the rotational speed of the compressor (22) reaches an upperreference value R2 in the cooling and cold thermal energy storageoperation, the controller (100) switches the operation from the coolingand cold thermal energy storage operation to the simple coolingoperation to reduce the rotational speed of the compressor (22). Theupper reference value R2 is set to be larger than R and smaller thanRmax.

In FIG. 12, for example, the efficiency of the compressor declines asthe rotational frequency exceeds R and approaches Rmax. In such a case,the efficiency of the compressor may be increased by switching theoperation from the cooling and cold thermal energy storage operation tothe simple cooling operation.

Further, the compressor (22) consumes more power when rotates at higherspeed. In view of this point, as well, it is recommended to switch theoperation from the cooling and cold thermal energy storage operation tothe simple cooling operation if the rotational speed exceeds apredetermined value.

Similarly to the lower reference value R1, the upper reference value R2is determined from the relationship between the rotational speed and theefficiency of the compressor, a rotational speed of the compressor (22)for storing cold thermal energy, and any other suitable parameters.

In order to store cold thermal energy in the thermal storage section(60), at least a certain amount of cold thermal energy is needed. Thus,in switching the simple cooling operation to the cooling and coldthermal energy storage operation, the rotational speed needs to beincreased at least by a value which allows for generation of the certainamount of cold thermal energy.

In this regard, the thermal storage section (60) may be designed to becapable of storing cold thermal energy by utilizing cold thermal energygenerated at a lowest rotational speed of the compressor (22). In thiscase, the simple cooling operation can be switched to the cooling andcold thermal energy storage operation by increasing the rotational speedof the compressor (22) by only the value of the lowest rotational speedof the compressor (22).

[Switching Between Simple Heating Operation and Heating and Warm ThermalEnergy Storage Operation]

Switching between the simple heating operation and the heating and warmthermal energy storage operation is performed in a similar manner to theabove-described switching between the simple cooling operation and thecooling and cold thermal energy storage operation.

In the simple heating operation, only the indoor air in the indoor heatexchanger (72) is heated, whereas in the heating and warm thermal energystorage operation, both the indoor air in the indoor heat exchanger (72)and the thermal storage medium in the thermal storage heat exchanger(63) are heated. Thus, the high pressure in the refrigeration cycle istemporarily lowered when the simple heating operation is switched to theheating and warm thermal energy storage operation.

On the other hand, in the simple heating operation and the heating andwarm thermal energy storage operation, the controller (100) adjusts therotational speed of the compressor (22) so that the high pressure in therefrigeration cycle (i.e., a pressure of the refrigerant discharged fromthe compressor) will be a predetermined target value. Thus, when thesimple heating operation is switched to the heating and warm thermalenergy storage operation, the rotational speed of the compressor (22)needs to be increased to raise the high pressure in the refrigerationcycle to the target value.

To do this, the controller (100) of the present embodiment switches theoperation of the thermal storage air conditioner (10) from the simpleheating operation to the heating and warm thermal energy storageoperation to increase the rotational speed of the compressor (22), ifthe rotational speed of the compressor (22) is slowed down to the lowerreference value R1 in the simple heating operation, and the compressor(22) starts to operate at an inefficient rotational speed. As a result,the rotational speed of the compressor (22) exceeds the lower referencevalue R1, and the efficiency of the compressor (22) is improved.

Conventionally, if the thermal storage air conditioner (10) has anexcessive heating capacity with respect to the heating load of the roomeven after the rotational speed of the compressor (22) is set to aminimum value Rmin, an on/off operation of the compressor (22), in whichthe halt and restart of the compressor (22) are repeated, is used to beperformed to prevent the room temperature from becoming too high.

On the other hand, the controller (100) of the present embodimentswitches the operation of the thermal storage air conditioner (10) fromthe simple heating operation to the heating and warm thermal energystorage operation, if the rotational speed of the compressor (22) isslowed down to the lower reference value R1 in the simple heatingoperation. With this control, the room can be heated by utilizing onlypart of the warm thermal energy obtained by the refrigeration cycle, andthe amount of the warm thermal energy used to heat the indoor air in theindoor heat exchanger (72) can be reduced to an appropriate amount forthe heating load in the room, while allowing the compressor (22) to keeprunning. Thus, according to the present embodiment, avoiding the on/offoperation of the compressor (22) allows for maintaining the comfort ofthe room high even in a state in which the heating load of the room isvery low.

Now, if the rotational speed of the compressor (22) reaches the upperreference value R2 in the heating and warm thermal energy storageoperation, the operation of the thermal storage air conditioner (10) isswitched from the heating and warm thermal energy storage operation tothe simple heating operation to slow down the rotational speed of thecompressor (22).

In FIG. 12, the efficiency of the compressor declines as the rotationalfrequency exceeds R and approaches Rmax. In such a case, the efficiencyof the compressor may be increased if the operation is switched from theheating and warm thermal energy storage operation to the simple heatingoperation. Further, the compressor (22) consumes more power when rotatedat higher speed. In view of this point, as well, it is recommended toswitch the operation from the heating and warm thermal energy storageoperation to the simple heating operation if the rotational speedexceeds a predetermined value.

Similarly to the case of cooling, the lower reference value R1 and theupper reference value R2 are determined based on the relationshipbetween the rotational speed and the efficiency of the compressor asshown in FIG. 12, a rotational speed of the compressor (22) for storingcold thermal energy, and any other suitable parameter.

In order to store warm thermal energy in the thermal storage section(60), at least a certain amount of warm thermal energy is needed. Thus,in switching the simple heating operation to the heating and warmthermal energy storage operation, the rotational speed needs to beincreased at least by a value that allows for generation of the certainamount of warm thermal energy.

In this regard, the thermal storage section (60) may be designed to becapable of storing warm thermal energy by utilizing warm thermal energygenerated at a lowest rotational speed of the compressor (22). In thiscase, the simple heating operation can be switched to the heating andwarm thermal energy storage operation by increasing the rotational speedof the compressor (22) by only the value of the lowest rotational speedof the compressor (22).

Variations of Embodiment

In the above-described embodiment, the check valve (CV1) is provided ata portion of the intermediate suction pipe (35) located outside thecasing (22 a) of the compressor (22). This configuration facilitates theconnection and maintenance of the check valve (CV1). The check valve(CV1) may be provided at the inner pipe portion (36) of the intermediatesuction pipe (35) located inside the casing (22 a). This configurationmay achieve a minimum channel length from the compression chamber of thecompression mechanism in the middle of the compression process to thecheck valve (CV1), thereby minimizing a dead volume that does notcontribute to the compression of the refrigerant. As a result, declinein the compression efficiency of compressor (22) may be prevented.

First Variant of Embodiment

It is recommended that the thermal energy stored in the thermal storagesection (60) during the cooling and cold thermal energy storageoperation and the heating and warm thermal energy storage operation inthe above-described embodiment be utilized when a cooling load or aheating load of a room is large. In other words, it is desirable thatthe thermal storage air conditioner (10) performs the utilizationcooling operation and/or the utilization heating operations (1) and (2)when the cooling load or the heating load of the room is larger than apredetermined value.

The broken line in the graph (a) of FIG. 13 shows a transition of thepower consumption of the thermal storage air conditioner according tothe first variant of the embodiment, and the solid line in the graph (a)shows a transition of the power consumption of a known air conditioner.As clearly shown in the graph (a) of FIG. 13, the thermal storage airconditioner according to the first variant of the embodiment consumesmore power at a low load, and less power at a high load, compared to theknown air conditioner.

In the first variant of the embodiment, the operation is switched fromthe simple cooling operation to the cooling and cold thermal energystorage operation when the load is low and the room needs to be cooled,and is switched from the simple heating operation to the heating andwarm thermal energy storage operation when the load is low and the roomneeds to be heated. On the other hand, the known air conditionercontinues the simple cooling operation when the load is low and the roomneeds to be cooled, and continues the simple heating operation when theload is low and the room needs to be heated. This is why, in the graph(a) of FIG. 13, the thermal storage air conditioner of the first variantof the embodiment, in which the cooling and cold thermal energy storageoperation or the heating and warm thermal energy storage operation isperformed, consumes more power at the low load than in the case wherethe simple cooling operation or the simple heating operation isperformed. As can be seen from this, although more power is consumedthan in conventional cases, cold thermal energy or warm thermal energycan be efficiently stored in the first variant of the embodiment.

Further, in the first variant of the embodiment, the utilization coolingoperation is performed when the load is high and the room needs to becooled, and the utilization heating operation is performed when the loadis high and the room needs to be heated. On the other hand, the knownair conditioner continues the simple cooling operation when the load ishigh load and when the room needs to be cooled, and continues the simpleheating operation when the load is high and the room needs to be heated.This is why, in the graph (a) of FIG. 13, the thermal storage airconditioner of the first variant of the embodiment, in which theutilization cooling operation or the utilization heating operation isperformed, consumes less power at the high load than in the case wherethe simple cooling operation or the simple heating operation isperformed.

In view of the power consumption at the low load and the high load, itcan be said that the power consumption is smoothed more in the firstvariant of the embodiment than in conventional cases.

The thermal storage air conditioner (10) according to the first variantof the embodiment may reduce variations in the indoor air temperature tokeep the comfort of the room, and reduce power consumption of the airconditioner (10).

It is recommended that the above-mentioned cooling or heating load inthe room be determined by the controller (100) based on data ofpredicted daily temperature transition, a peak temperature value in saiddata, annual data of temperature transition, etc.

Second Variant of Embodiment

In the graph (b) of FIG. 13, the curves show the efficiency of thethermal storage air conditioner (10) with respect to the transition ofload factors with respect to a rated capacity, and the bar charts showoperational time of the thermal storage air conditioner (10) withrespect to the transition of the load factors with respect to the ratedcapacity, separately for the heating operation and the coolingoperation.

The bar charts in the graph (b) of FIG. 13 reveal that the maximum loadfactor with respect to the rated capacity is 100% in a coolingoperation, but 70% in a heating operation. The bar charts in the graph(b) of FIG. 13 further reveals that in both of the cooling operation andthe heating operation, about 90% of the annual operation time isdirected to the load factor of 50% or less.

In view of this, in general, the thermal storage air conditioner (10)which can deal with the largest load factor (i.e., 100%) in the coolingoperation is selected. However, as shown in the bar charts in the graph(b) of FIG. 13, the length of time in which the load factor is at themaximum (i.e., 100%) is very short, i.e., about several hours a year,even in the cooling operation.

On the other hand, the thermal storage air conditioner (10) according tothe above-described first variant of the embodiment may perform theutilization cooling operation when the cooling load in the room is high,and may perform the utilization heating operation when the heating loadin the room is high. That is, the thermal storage air conditioner (10)according to the first variant of the embodiment may perform theutilization cooling (or utilization heating) operation to deal with highload factors. Thus, in selecting the thermal storage air conditioner(10) of the first variant of the embodiment, the thermal storage airconditioner (10) smaller in size (i.e., horsepower) than the airconditioners usually selected may be selected. For example, according tothe first variant of the embodiment, it is possible to select an 8horsepower (HP) thermal storage air conditioner which is smaller in size(i.e., horsepower) than a 10 HP thermal storage air conditioner, in asituation in which a 10 HP thermal storage air conditioner is supposedto be selected.

In the graph (b) of FIG. 13, the solid curve shows the transition of theefficiency with respect to the load factor of the 10 HP thermal storageair conditioner, and the broken curve shows the transition of theefficiency with respect to the load factor of the 8 HP thermal storageair conditioner. The comparison between the two curves shows that thethermal storage air conditioner smaller in size (i.e., horsepower) hasgreater efficiency than the thermal storage air conditioner larger insize (i.e., horsepower) at low loads.

That is, according to the thermal storage air conditioner (10) of thefirst variant of the embodiment, the efficiency at low loads (at which alarge part of operations is performed) is increased, and the annualefficiency may thus be improved, by selecting the thermal storage airconditioner (10) smaller in size (i.e., horsepower) than the usuallyselected thermal storage air conditioner.

Third Variant of Embodiment

The thermal storage sections of the above embodiments are so-calleddynamic thermal storage devices having a thermal storage circuit inwhich the thermal storage medium is circulated. However, the thermalstorage sections may be so-called static thermal storage devices inwhich water or other thermal storage media retained in a tank, forexample, is allowed to exchange heat with a refrigerant.

INDUSTRIAL APPLICABILITY

As can be seen from the foregoing description, the present invention isuseful as a thermal storage air conditioner.

DESCRIPTION OF REFERENCE CHARACTERS

-   10 Thermal Storage Air Conditioner-   11 Refrigerant Circuit-   22 Compressor (Compression Section)-   23 Outdoor Heat Exchanger-   28 Suction Pipe (Low-Pressure Suction Portion)-   31 First Introduction Pipe (Low-Pressure Introduction Pipe)-   32 First Subcooling Heat Exchanger (First Heat Exchanger)-   35 Intermediate Suction Pipe (Intermediate Suction Portion)-   36 Inner Pipe Portion-   44 Primary Thermal Storage Channel-   60 Thermal Storage Section (Thermal Storage Device)-   61 Thermal Storage Circuit-   62 Thermal Storage Tank-   63 Thermal Storage Heat Exchanger-   65 Outflow Pipe (Outflow Portion)-   72 Indoor Heat Exchanger-   100 Controller (Operation Control Section)-   EV1 First Decompression Valve (Decompression Valve)

The invention claimed is:
 1. A thermal storage air conditioner,comprising: a refrigerant circuit which has a compressor, an outdoorheat exchanger, and an indoor heat exchanger and performs arefrigeration cycle; a thermal storage section which has a thermalstorage medium and exchanges heat between the thermal storage medium anda refrigerant of the refrigerant circuit; and a controller configured tocontrol the refrigerant circuit such that the thermal storage airconditioner performs a simple cooling operation in which in therefrigerant circuit, the refrigerant is condensed in the outdoor heatexchanger and evaporates in the indoor heat exchanger; and a cooling andcold thermal energy storage operation in which in the refrigerantcircuit, the refrigerant is condensed in the outdoor heat exchanger andevaporates in the indoor heat exchanger, and in which the thermalstorage medium in the thermal storage section is cooled by therefrigerant; and switch, if a rotational speed of the compressor isslowed down to a predetermined lower reference value during the simplecooling operation, operation of the thermal storage air conditioner fromthe simple cooling operation to the cooling and cold thermal energystorage operation to increase the rotational speed of the compressor. 2.The thermal storage air conditioner of claim 1, wherein the controlleris further configured to switch the operation of the thermal storage airconditioner from the cooling and cold thermal energy storage operationto the simple cooling operation to reduce the rotational speed of thecompressor if the rotational speed of the compressor increases to apredetermined upper reference value during the cooling and cold thermalenergy storage operation.
 3. The thermal storage air conditioner ofclaim 1, wherein when the controller switches the operation of thethermal storage air conditioner from the simple cooling operation to thecooling and cold thermal energy storage operation, the rotational speedof the compressor is increased by a value equal to a lowest rotationalspeed of the compressor.
 4. The thermal storage air conditioner of claim2, wherein when the controller switches the operation of the thermalstorage air conditioner from the simple cooling operation to the coolingand cold thermal energy storage operation, the rotational speed of thecompressor is increased by a value equal to a lowest rotational speed ofthe compressor.